Wastewater streams containing organic and/or inorganic contaminants present a disposal problem for many industries. Non-limiting examples of such industries include agricultural, petrochemical, pharmaceutical, food processing, paper-mill, textile, and landfill industries. Contaminants found in these streams are typically undesirable organic compounds, including hydrocarbons, that must be removed, or decomposed, to an appropriate level prior to releasing the stream into the environment. Increasingly stricter environmental regulations demand increasingly higher standards for treating wastewater streams.
The food processing industry, for example, is in need of cost-effective treatment technologies for removing organic matter, measured as biochemical oxygen demand (BOD), and nitrogen from food processing wastewater streams that often contain relatively high levels of suspended solids and nitrogen compounds.
Enforcement of wastewater discharge regulations and escalating sewage surcharges have forced the food processing industry to look for cost-effective technologies for providing pretreatment, or complete treatment, of their wastewater streams. Historically, food processors located within or adjacent to municipalities have relied on local publicly owned treatment works for their wastewater treatment and disposal. Increasingly, this option is becoming less available. Because of dwindling federal grants for constructing new and upgrading existing publicly owned treatment works, municipal and regional sewer authorities are applying more pressure on private industries to reduce their organic, BOD and chemical oxygen demand (COD), and solids loading to sewers. Food processing wastewaters are particularly targeted because of their high BOD concentrations, especially high-strength wastewaters having high levels of suspended solids, ammonia and protein compounds. Thus, food processors are in need of cost-effective and application-specific treatment technologies to more effectively manage their wastewater streams.
The primary means of reducing BOD in food processing wastewater streams, as well as waste streams from many other industries, is by biological treatment. Biological treatment for such streams are typically categorized as aerobic, anaerobic, or a hybrid wherein a sequential aerobic-anaerobic treatment is used. Each such method can be either thermophilic or mesophilic. Non-limiting examples of aerobic technologies include trickling filter, activated sludge, rotating biological contactors, oxidation ditch, sequencing batch reactoras well as controlled wetlands. A bioreactor operated at mesophilic conditions will typically be operated within a temperature range of about 5 to 40° C., whereas a bioreactor operated at thermophilic conditions will be operated at about 55°±10° C.
While bioreactors, such as thermophilic bioreactors, have been proposed for the treatment of wastewater streams, they still face considerable challenges, such as a way to effectively maintain a desired temperature range of the biomass during operation.